Attaching a skull cap back to the head
One way you could do it is join them together (Cntrl J) and then you can bridge the vertices by bridging edge loops, you could also join them and the line the cap as close as you can to the mesh in edit mode and then remove duplicate vertices. this will reconnect them. If you don't have a whole lot of corners to connect you could always merge vertices one at a time, with alt m. If you want further help on how to perform any of these functions just ask. If you are wondering how to connect them and continue using the particle system, just use the same particle settings on the new mesh but use a vertex group of the scalp for the density slot under vertex groups in particle settings.